This invention relates to grids or gratings useful for bridge decks, walkways, drain gratings and the like and more particularly, this invention relates to concrete overlaid grids or gratings that are constructed and held together without welding.
In making prior gratings for bridge decks, whether the deck is open or filled with concrete, a certain amount of welding is performed to hold or bind the individual components together. That is, if the grid is used for open grating or open bridge deck, the main load-bearing members, secondary load-bearing members and tertiary load-bearing members are welded together, usually by puddle welding, to hold the members together and give the deck or grating strength. Even if the grid or deck is to be encased in concrete, still some welding is required to hold the assembly in a rigid configuration until the concrete hardens. If only minimal welding is performed, then the deck or grid work when encased in concrete has a decreased level of strength. Thus, for peak bridge strength, the various components of the grating or bridge deck must be fastened together to perform as a unit. When a concrete wear layer is provided on top of the grid, it is very important that the wear layer is securely fastened to the grid to provide for high strength.
Various deck or grating systems have been proposed in the art, and the members comprising the grating deck are welded together. For example, U.S. Pat. No. 3,260,023 discloses a bridge floor and surfacing component. The bridge floor comprises parallel bearer bars and cross bars. The cross bars are pressure welded into the tops of the bearer bars.
U.S. Pat. No. 4,865,486 discloses a method of assembling a steel grid and concrete deck wherein the primary load bearing bars are formed with openings to receive slotted secondary load bearing bars that are passed through the primary load bearing bars. However, the patent discloses that tack welds are used to temporarily hold the grating in its desired configuration. A concrete component encases at least the top surface of the grating base member and secures the elements of the grating base member together.
U.S. Pat. No. 2,128,753 discloses a steel floor construction having a series of parallel main bars in spaced relationship. Each of the main bars is provided with a plurality of rectangular-shaped openings. The openings are designed to permit the insertion thereon and the positioning of two cross bars. A third set of bar is placed in slots in the cross bars. After the members are assembled, the entire construction may be welded together to maintain the different parts in position.
U.S. Pat. No. 2,190,214 discloses a grating wherein a desired number of parallel spaced apart main bearer bars with intermediate bearer bars of less depth are placed between the main bearer bars. The main bearer bars and intermediate bearer bars are connected at their tops by cross bars secured thereto by electric pressure welding. Carrier bars which pass through slots in the main bearer bars are welded to the intermediate bearer bars. Also, carrier bars are welded to the main bearer bars.
U.S. Pat. No. 2,645,985 discloses an open floor grating having a plurality of longitudinal primary members, a plurality of transverse secondary members welded to and extending between the primary members. A plurality of tertiary members are welded to the secondary members. A rod is inserted through holes in the webs of the primary members and welded thereto.
U.S. Pat. No. 2,834,267 discloses a grating comprised of a plurality of spaced parallel main longitudinal bars and a plurality of spaced parallel lacing bars and tertiary longitudinal bars intermediate the main bars. Bottom bars are inserted through holes in the webbing of the main bars. The intersection between the lacing bars and the tertiary bars are welded and the bottom bar is welded to the webbing of the main bar.
U.S. Pat. No. 4,452,025 discloses a self-interlocking grille consisting of a plurality of metallic or plastic strips or flats or bars with certain types of notches and holes disposed along the length of the strip or flats or bars in a regular interval, which are used together with a plurality of rods in assembling a variety of interlocking grills.
U.S. Pat. No. 4,780,021 discloses an exodermic deck conversion method for converting a conventional grid deck to an exodermic deck. Tertiary load bearing bars are placed on top of the grating parallel to and between the primary load bearing bars. A plurality of shear connectors, such as vertical studs, are welded or attached to the surface of the grating. It will be seen from the above that in gratings and bridge decks, usually some form of welding or cement is used to hold the assembly together.
U.S. Pat. No. 4,865,486 discloses a weldless pavement module and a method for making a weldless pavement module. Each of the primary load bearing bars is formed with openings for receiving slotted secondary load bearing bars which are passed through the primary load bearing bars in a substantially horizontal position and which are rotated into a vertical position. The size and shape of the openings and the slots permit the combination of primary load bearing bars and secondary load bearing bars to be skewed to form a nonrectangular parallelogram configuration. Simple tack welds are used to temporarily hold the grating in its desired configuration.
U.S. Pat. No. 5,509,243 discloses a deck for structural floors including bridge floors, road beds, pedestrian walkways, or the like, comprises a composite structure of a grid component and a top component. The grid component is preferably made of steel and includes a plurality of main bearing bars and a plurality of distribution bars oriented perpendicular to the main bearing bars. The top component is preferably made from reinforced concrete. The upper portions of either the main bearing bars or the distribution bars are embedded in the reinforced concrete component permitting horizontal shear transfer and creating a composite deck structure which maximizes the use of tensile strength of steel and the compressive strength of concrete.
U.S. Pat. No. 5,454,128 discloses a prefabricated metal deck form to provide bridge deck construction and/or bridge deck replacement. The construction is simplified to both shorten construction time and to save on construction costs. The deck form, including a concrete slab is sufficient to sustain both dead loads and heavy, live loads on a bridge.
However, welding gratings or deck structures have the problem that toxic fumes are released into the atmosphere causing health hazards to the welders and pollution of the environment. Welding of structures such as bridge decks results in curling or deforming of the deck as the welds cool. Thus, the design of the deck is complicated in that the curling or deforming must be accommodated in the design. Further, welding has the disadvantage that it is time consuming and often is the rate-determining step at which decks can be built. Welding also requires that the gratings or deck assemblies be maintained in jigs prior to starting the welding process. This is an additional, undesirable step in the process of making a bridge deck. Further, welds on bridge decks have the problem of cracking either with use or as the temperature cycles between winter and summer. It is desirable to rustproof gratings by galvanizing. However, because galvanizing is destroyed by welding, the welded grating or deck is often galvanized as a unit. However, this also results in temperature cyclization and warping of the bridge deck with the result that welds often break, detrimentally affecting the integrity of the deck.
Thus, it will be seen that there is a great need for an improved bridge deck or grating which will eliminate these problems and will provide for an improved deck or grating structure. The present invention provides such a structure.